Air dryer construction and method of operation



4 Sheets-Sheet. 1

Jan. 13, 1959 P. H. BRANDT AIR DRYER CONSTRUCTION AND METHOD OF' OPERATION Filed ont. 14,(1955 Jan. 13, 1959 P. H. BRANDT 2,867,988

AIR DRYER CONSTRUCTION AND lMETHOD oF OPERATION Filed oct. 14, 1955 4 sheets-sheet 2 Q F/G. 2

Jan. 13, 1959 PrH. BRANDT AIR DRYER CONSTRUCTION AND METHOD OF' A,OPERTION Filed oct. .14. 1955 4 Sl'xeets-Sheei'l 3 ATTR/VEY P, H. BRANDT AIR DRYER CONSTRUCTION AND METHOD OF' OPERATION Filed OCC. 14, 1955 4 Sheets-Sheet 4 mDOI ms: I

ATTORNEY AIR DRYER CONSTRUCTION AND METHOD F OPERATION .Paul H. Brandt, Park Ridge, Ill.

Application October 14, 1955, Serial No. 540,537l

4 Claims. (Cl. 62-93) My invention relates to an improved air dryer capable of continuous operation to produce air of very low dew point without interruption and to the construction thereof.

One of the conventional methods of drying, or conditioning, air is to pass it through a cooled chamber or heat exchanger. The chamber has a refrigerating system, including coils within the chamber which carry a circulating refrigerant. The evaporation of the refrigerant lowers the temperature of the air in the chamber below the dew point of the moisture, oil, or other condensible to be removed. The condensate forms a frost inside the chamber which accumulates on the cooling coils. As the operation continues, this frost progressively reduces heat flow and impedes the cooling action of the coils. Ultimately it is necessary to raise the temperature in the chamber to melt the frost. In conventional units the air drying process must be inter- United States Parent O rupted until the cooling coils are restored to their unfrosted condition.

In the apparatus of the present invention the a-ir is passed alternately through a pair off heat exchangers disposed in tanks. The air travels at high pressure in good heat exchange relation through the respective tanks because of vertical bafe elements which drive the air over the horizontal cooling coils in `a plurality of passes. The tanks each contain heaters which are energized in sequence with the iiow of air and evaporating refrigerant lin a cycle assuring that when air flow is passed `through each tank it is in eiective condition to receive air to be cooled. The air is passed through the heat exchangers 'at high pressure. In this condition it has a relatively high dew point, so that condensation takes place within the tanks at a comparatively high temperature such as 0 F. When the air is subsequently permitted to expand the dew point falls, thus providing air vat a very low dew point, such as ,100 F;

It is therefore a general object of the present invention to provide an improved method of and apparatus for drying air.

It is another object of the present invention to provide an improved air dryer of the alternate ow type in which defrosting is automatically accomplished without the interruption of air flow.

It is yet another object of the present invention to provide an improved air dryer having coordinated heating and cooling means in alternately operated chambers to achieve effective continuous operation.

Additionally it is an object of the present invention to provide an improved air dryer having a pair of air cooling vchambers through which the air is alternately propelled at a comparatively high pressure, together with means to close off the unused chamber while warming v icc provide continuous operation and to assure that each chamber is prepared to receive air at the time the air conducting portion of the cycle takes place.

Yet another object of the present invention is to provide Aan improved heat exchanger construction for an air dryer, wherein a plurality of bafes cooperate with both heating and cooling coils to provide effective heat transfer as well as mechanical support.

Still another object of the present invention is to provvide an air dryer of the foregoing type having a simple,

inexpensive and yet highly elective construction for achieving the requisite heat transfer and for discharging periodically the accumulated condensate.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:

Figure l is a schematic drawing in perspective, showing the units of the present invention and the ow of air, water, ,and refrigerant between the units;

Figure 2 is a View from the side with parts broken away of the apparatus of Figure l;

Figure 3 is an end elevational view of the apparatus of Figure 1 as seen from the right hand end, through axis 3 3 of Figure 2;

Figure 4 is a cross-sectional view through axis 4 4, Figure 2, with parts in top plan view for clarity;

Figure 5 is a fragmentary cross-sectional view through axis 5 5, Figure 2;

Figure 6 is a cross-sectional view through axis 6 6, Figure 2;

Figure 7 is a schematic circuit diagram of the control mechanism for the apparatus of Figures 1-6; and

Figure 8 is a time chart showing the sequential energization of the several units of the air dryer in two four -hour cycles of operation.

As shown in Figures 2 and 3 the apparatus of the (present invention is housed in a cabinet 10 having an upper ycompartment 12 and a lower compartment 14. The apparatus consists of two tanks 16 and 18, Figure 3, cooled alternately by la refrigerating system, hereinafter described, under the control of an electrically operated timer control system which also serves to condition each tank for successive cooling operation. The refrigeration and control mechanism is primarily located in the lower compartment 14. The tanks and air treatment system are located in upper compartment 12.

Construction Two similarly constructed tanks of steel or the like,

16 and 18, are located in the upper compartment 12 ofV the cabinet as shown in Figures 2 and 3.4 These are preferably of circular cross-section as shown. Tank 16 is shown in detail in Figures 4, 5 and 6 and it will be understood that the other tank is similarly constructed. Accordingly the following description is confined to tank 16. The tank 16 has a cylindrical body 20 with rounded closures 22 and 24 at the opposite ends vas shown in Figure 4. The pipes defining cooling coils 26L enter the drying chamber through a series of aligned openings in the upper part of closure 22, and extend the length of the tank 20. The coils 26L double back at 27L, Figure 4, to pass back along the central portion of the chamber immediately below the initial portions of the coils. Each coil is repeatedly doubled back upon itself, in vertical alignment, before passing out of the tank through `the lower part of closure 22, as shown in Figures 2, 4, 5 and 6.

The cooling coils are supported in the body 20 of the tank by a series of baille plates 28 and 38 which upstand alternately from the top and bottom of the body 20 of the tank as shown in Figures 2, 4, and 5. The baffles extend laterally, normal to the longitudinal axis of the tank, between'two vertical longitudinal'plates 31, as shown in Figures 4, and 6. Each of the plates 31 extends from the top to the bottom of the cylindrical tank. Each baffle has one side in the shape of a segmental circle with its circular edge forming a snug fit withthe Wall of the cylindrical body. The opposite side of each bafe plate extends horizontally as shown. A series of holes in the `baffle plates carries the cooling coils 26L. With the baffle plates extending laterally between the spaced plates 31, a substantially horizontal space through which the cooling coils pass is defined by the two vertical longitudinal plates 31 and the planes of the lower edges of baffle plates 30 and the upperedges of baie plates 28. The bafe plates 28 and 31) are made of a good heat conducting material, such as copper, and, in addition to diverting the flow of air through the chamber, serve as `enlarged fins on the cooling coils. A series of smaller fins 32, Figure 4, made of a suitable heat conducting material, such as copper, are received onthe coils 26L inside the chamber to provide further increased heat transfer.

The lower batiie plates 28 extending upwardly from the bottom of the tank have a bottom U-slot S0 formed in their circular edges opposite the horizontal straight edge of the baffle plate, as shown in Figure 5. These slots are in alignment and coincide with the vertical axis of tank 16. An electrical heating element 52L is carried in the upper portion of the slots, as shown in Figure 5, and extends the length of the tank 16 as shown in Figure 2. The heating element is energized by suitable electrical conductors which pass through the tank at a convenient location (not shown), a suitable insulating plug being provided for this purpose. The slots 50, which extend from the heating element S2L to the lower edge of the body of the cylindrical tank 16, further serve as a drainage passage for the melted frost. In order to achieve proper drainage the tanks 16 and 18 are mounted on supports S7 and S9 with the longitudinal axes of the tanks inclined at an angle. Drain pipes S4L `and 54E are connected to the tanks 16 and 18, respectively, at their lower ends, as shown in Figures 2 and 3. Flow from the tanks throughl the drain pipes is regulated by solenoid valves 68 and 70, located in lines S4L and S4R respectively, as shown in Figure 3.

It will be noted that the depending baffles 30 are secured in place by attachment to the vertical longitudinal plates 31. In consequence, these baffles serve to supplement the support of the cooling coils achieved from the upstanding lower baffles 28.

The cooling coils 26L and 261?. inside the tanks 16 and 18, respectively, are a part of a refrigerating system shown in Figures 1, 2 and 3. Gaseous refrigerant pipes 34L and 34R are connected to the cooling coils 26L and 26R, respectively, at their outlet from the tanks 16 and 18 to carry the gaseous refrigerant evaporated in tanks 16 and 18 to the heat exchanger 36. The gaseous refrigeranthere serves to cool liquid refrigerant from pipe 4S on its return path to the tanks 16 and 18. Pipe 34 carries the refrigerant from the heat exchanger 36 to the compressor 38. Thecompresscd refrigerant vapor is passed to the water cooled condenser 40 through pipe 42. The condenser receives water from a source (not shown) through pipe 41 and discharges the water through pipe 43. The cooling action of the water serves to extract heat from and condense the refrigerant which at this point in the system is at high pressure. Liquid refrigerant leaving the condenser 40 is carried through the heat exchanger 36 to be further cooled and then to expansion valves 44 and 46 adjacent the tanks 16 and 18 by pipe 48, and its extensions 48L and 48k, all as shown in .4 Figure l. The cooling coils 26L and 26R receive refrigerant-from the expansion valves 44 -and 46, respectively. The ow of refrigerant through the cooling coils is controlled by solenoid valves 64 and 66 which are located in lines MBL and 48R, respectively, in the manner hereinafter described.

Air under a relatively high pressure from the reservoir 90, Figure 1, is delivered through pipe S6, and extensions S6L and 5'6R to be discharged into tanks 16 and 18, respectively. The processed air from the tanks 16 and 1S is carried by air outlet pipes SSL and SSR which are connected to the single header pipe S8. Check Valves SQL and S9R are located in lines SSL and SSR, respectively, to arrest reverse air flow. The flow of air through the air dryer is controlled by means of two solenoid operated valves 60 and 62. Valve 60, located in pipe line 56L, regulates the air passing into the tank 16 while valve 62, located in line S6R, performs the same function for tank 18, all as hereinafter described in detail.

The air to be dried is compressed by compressor 92 and discharged to the storage tank 90. The air pressure -at this point may, for example, be 200 pounds per square inch.

The electrical circuit for the air dryer is shown in Figure 7. Alternating voltage from source 73 is supplied to the primary 72a `of transformer 72 and drawn from the secondary 72b at 110 volts and 220 volts. The two heaters S2L and S21?` are selectively connected across the full secondary 72b of the transformer and are energized through relays 74 and 76 respectively. The switch elements 74a and 76a of relays 74 and 76 are operated by the relay solenoids 74b and 76b, respectively, connected across the Volt line by the timer hereinafter described.

The timer includes a motor 82 which is constantly energized from one half of secondary 72b. It has three sets of single pole double throw switch elements 84, 86 and 88, which are actuated by a timer motor 82. The double throw switch element 84 has common terminal 84a which may be selectively connected to either terminal 84h, connected to the solenoid 60a of the air valve .60, or 84C connected to the solenoid 62a of air valve 62.

The double throw switch element 86 has common terminal 86a which may be selectively connected either to terminal 86h or terminal 86C. The solenoid 64a of the refrigerant solenoid valve 64 connects to terminal 86h. The solenoid 68a of the drain solenoid valve 68 and the solenoid 74b of relay 74 are connected to terminal 86e. The double throw switch element 88 has terminal 88a which may be selectively connected either to terminal 88h or 88C. Terminal 88E connects to solenoid 66a of refrigerant solenoid valve 66 and terminal 88a` connects both to solenoid 70a of drain solenoid valve 70 and solenoid 76h of relay 76.

It will be noted that -when any of the windings or solenoids 74, 76, 60a, 62a, 64a, 66a, 68a or 70a is connected through its respective switch element 84, 86, or 88 the voltage appearing across one half of the secondary '72b is applied to it. Thisis, say, 110 volts, and is adequate to cause operation of the respective relays and solenoids. The time sequence of operation of the switches 84, 86 and 88 is described in detail hereafter.

The actuation of the switches 84, 86 and 88 by motor 82 may be accomplished by any one of many methods known to the art. Preferably the motor 82 drives a series of cams, one for each switch. The switches are single pole double 'throw pressure actuated switches physically connected to cam follower elements riding on the cams, respectively. Each cam is provided with large and small radius portions which serve, through the cam followers, to actuate the switches to one position or the other in accord with the desired time cycle, hereinafter described.

Operation Throughout the entire cycle high pressureair from the reservoir 90, compressed by compressor unit 92, is made available to the dryer through pipe S6 as shown in Figure 1. This pressure may, for example, be 200 pounds per square inch. At this pressure the water, oil, and other condensibles are condensed on the heat exchanger at, say, 0 F., and are removed to an extent that provides a much lower dew point, say 100 F., when the air pressure is reduced to approximately atmospheric pressure.

The chart in Figure 8 shows the'sequential operation of the units of the air dryer under the control of the timer switch. The chart is based on a time cycle of four hours, which has been found to give satisfactory results, and shows two complete cycles. The time periods during which each unit is energized through its respective time switch is shown by the bars of the chart.

At the beginning of the cycle the double throw switch 84 is in the position of Figure 7 where it connects terminals 84a and. 84h. This energizes the solenoid 60a in valve 60 and deenergizes the solenoid 62a of valve 62, (see Figure 7). This opens valve 60 and closes valve 62, directing all the compressed air fed through pipe 56 through pipe 56L and into tank 16 and arresting air flow through pipe 56R. At this time the two way switch 86 is already closed between terminals 86a and 88b, as shown in Figure 7, so that solenoid 64a of switch 64 is energized, permitting refrigerant to flow through coils 26L of tank 16. The solenoid 68a to the drain valve 68 oftank 16, connected to the other terminal 86e of switch 86, is necessarily deenergized, and the valve closed, thus sealing the interior of tank 16 for air ow between inlet pipe 56L and outlet pipe SSL. For the same reason, the solenoid 74b of relay 74 is deenergized and the heater -relay switch 74 is open to deenergize heater 52L of tank 16 so that the only action therein is the 'cooling action of the evaporating refrigerant in pipes 26L.

At the beginning of the cycle double throw switch 88 is thrown, by the timer motor 82, to the position shown in Figure 7. In this position it connects terminals 88a and 88C, thus energizing the solenoid 70a of drain valve 70 and the solenoid 76b of relay 76. This opens the drain valve 70 of tank 18 and energizes the heater 52R of tank 18. At the same time the refrigerant valve solenoid 66a connected to terminal 88b, is deenergized. Thus the cooling action in tank 18 is stopped and defrosting in that chamber initiated.

The air passes through tank 16 and to the lowerpressure outlet through discharge pipes 58L and 58. It should benoted that the check valve S9R in pipe line SSR prevents the discharge air from feeding back into the tank 18. The alternately spaced upper and lower bales 28 and 30, shown in Figure 2, force the air to cross the cooling coils 26L at frequent intervals in a sinuous path, to increase the heat transfer from the warmer air to the cooler pipes. This is shown by the arrows of Figure 2. The air in the chamber is reduced to a temperature below its dew point at the pressure of the air in the chamber, causing the moisture in the air to condense and form solid frost on the pipe 26L and the baffles. Also other condensibles, such as oil, condense out, either as liquid which flows to the bottom of tank 16, or as solid frost which deposits on the cooling surfaces.

While tank 16 is thus serving as a drying chamber for the air from tank 90, Figure l, the chamber defined by tank 18 is being conditioned for subsequent like operation. It will be noted that at the instant the cycle commences the heater 54R is energized and drain solenoid 6 less than an hour and fteen minutes for each tank. Consequently, after this period has passed the tank is known to be free from frost and liquid condensate.

After one hour and fifteen minutes of the cycle, switch l88 is thrown by the timer motor 82 from terminals 88e to terminal 88b. This deenergizes the solenoid 76b of relay 76, causing the circuit containing heater 52R to open. Simultaneously the solenoid 70a of drain valve 70 is deenergized to close that valve. This terminates the defrosting and draining action in chamber 18. At the same time refrigerant solenoid 66a is energized, opening valve 66, to permit the refrigerant to flow through tank 18. This serves to cool tank 18 in preparation for the receipt of air. Processing of air in tank 16 is unaltered at this time.

At two hours, double throw switches 84 and 86 are thrown by the timer motor 82 to the positions opposite those shown in Figure 7. Switch 84 is thrown from terminal 84b to 84C, deenergizing solenoid 60a of air valve 60 and energizing solenoid 62a of air valve 62. This stops the air from flowing into tank 16 and causes it to pass through tank 18, which, by this time, is cooled to receive the air. Switch 86 is thrown from terminal 3611 to 86e which deenergizes solenoid 64a of refrigerant valve 64. The solenoid of drain Valve 68 is energized simultaneously with solenoid 74b of relay 74. This stops the ow of refrigerant in tank 16 and initiates the defrosting action in that tank by opening the drain valve and starting the heater.

At this timethe cycle has reached the half way point where the air drying takes place in tank 18 and tank 16 is ready to undergo conditioning for a later cycle.

At three hours and fifteen minutes the double throw switch 86 is thrown from terminal 86C to 861; to energize solenoid 64a of refrigerant valve 64. At the same time the relay solenoid 74b and the drain valve solenoid 68a are deenergized. This causes refrigerant to start flowing again through the cooling coils of tank 16 and stops the heater and closes the drain valve in that unit. Thus, the cooling of tank 16 is commenced to prepare it for the receipt of air at the beginning of the next cycle while the air processing, and cooling, continues in tank 18.

The air discharged at high pressure into the pipe 58 is carried to apparatus where it is permitted to expand for use at lower pressure. Such apparatus may, for example, include air expansion valve 59, Figure l, which feeds the air to the apparatus in which it is used. The valve 59 may be a simple throttle valve which serves to reduce the air pressure from the relatively high pressure at which drying takes place to the low pressure-which may ybe only slightly above atmospheric-at which it is used. If desired, a low pressure air storage tank (not shown) may be provided. Also the normal pressure drops in the air using system and control valves may be utilized to ex' pand the dried air.

It will be apparent from the foregoing that the apparatus of the present invention serves continuously to dry air from tank 90. Also this action occurs at a high pressure developed by compressor 92, which assures that upon subsequent air expansion the dew point will be further lowered from that in the high pressure pipe 58. Additionally the construction of the tanks 16 and 18 and their interior pipes and baies serves to provide a readily manufactured, simple, and reliable unit.

While I have shown and described a specic embodiment of the present invention, it will, of course, be understood that various modifications and alternative constructions may be made without departing from the true spirit and Scope thereof. Thus, for example, the heating of each tank may be during only part of the time refrigerant is not supplied thereto, or the time periods of the 'cycle may be altered. Specifically, the length of the cycle, and the various phases of the cycle, can be altered to accommodate the capacity of the equip- Y'-7 ment and other conditions without departing from the invention. I Ytherefore intend by the appended claims to cover all such modifications and alternative constructions falling within their true spirit and scope.

What I claim as new and desire to secure lby Letters Patent of the United States is:

1. An apparatus for drying air comprising in combination: first and second drying tanks each having a heater and a cooling coil; a source of refrigerant; means to circulate refrigerant through either tank singly or both tanks simultaneously; means to regulate the circulation of refrigerant in a four .part cycle to cause it to flow at Successive time periods through the first tank, through both tanks, the second tank, and then through Iboth tanks; means to energize the heater of each tank during at least a portion of the time refrigeration is not applied thereto; and means to pass air through the said one tank during the first two parts of the cycle and through the said other tank during the last two parts of the cycle.

2. The method of operating a two part dryer having first and second air treating chambers each having a cooling means and a heater comprising the steps of: first, passing air through the first chamber while energizing the cooling means `of the same and while the heating means of the second chamber is energized; second, continuing the passage of air through the first chamber and energization of the cooling means thereof, while energizing the cooling means of the second chamber; third, passing air through the second chamber while energizing the cooling means of the same and while the heating means of the first chamber is energized; and fourth, passing air through the second chamber while energizing the cooling means of the same and while the cooling means of the first chamber is energized, the whole being carried out at time intervals suiiicient to remove the frost and condensate from each chamber to prefcool the same to normal air drying temperature before air is passed therethrough.

3. An apparatus for drying air comprising in combination: first and second drying tanks each having a heater, a cooler to receive refrigerant, air inlet and outlet passages, and a condensate drain passage; dried air outlet means connecting the outlet passages of the tanks; one way valves interposed between said outlet passages, respectively, and the air outlet means to arrest back flow of air from the a'ir outlet means to either drying tank; and means to regulate the `operation of the said tanks in a four part cycle, during the first part of which refrigerant and air to `be dried flow through the first tank, the drain passage thereof is closed, and while in the second tank the condensate drain passage is open and the heater is energized, during the second part of which refrigerant flows through both tanks, both condensate drain passages are closed, and air flows through the first tank, during the third part of which refrigerant and air to be dried flow through the second tank, the drain passage thereof is closed, and while in the first tank the condensate drain passage is open and the heater is energized, and during the last part of which refrigerant flows through both tanks, the condensate drain passages are both closed, and air fiows through the second tank.

4. An apparatus for drying air to a comparatively low dew point comprising in combination: means to compress the air; first and second drying tanks each having a. heater, a cooler to receive refrigerant, air inlet and outlet passages, and a condensate drain passage; dried air outlet means connecting the outlet passages of the tank; an air expansion means connected to said last means to reduce the pressure and dew point of air discharged therefrom; one way valves interposed between said outlet passages, respectively, and the air outlet means to arrest back flow of air from the air outlet means to either drying tank; `and means to regulate the operation of the said tanks in a four part cycle, during the first part of which refrigerant and air to be dried fiow through the first tank, the drain passage thereof is closed, and while in the second tank the condensate drain passage is open and the heater is energized, during the second part of which refrigerant flows through both tanks, both condensate drain passages are closed, and air flows through the first tank, during the third part of which refrigerant and air to be dried fiow through the second tank, the drain passage thereof is closed, and while in the first tank the condensate drain passage is open and the heater is energized, and during the last part of which refrigerant ows through both tanks, the= condensate drain passages are both closed, and air flows through the second tank.

References Cited in the le of this patent UNITED STATES PATENTS 1,004,468 Reynolds et al. Sept. 26, 1911 1,853,236 Shadle Apr. 12, 1932 2,281,168 Paget Apr. 28, 1942 2,496,143 Backstrom Ian. 31, 1950 

